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Radwanski, Diane. Physiology and carbon allocation of two co-occurring poplar species (Populus deltoides and Populus tremuloides) in an urban brownfield. Retrieved from https://doi.org/doi:10.7282/T31G0PGS

DescriptionPhytoremediation is a technique to reclaim heavy metal-contaminated soils which has increasingly gained interest, and an understanding of plant physiological responses to heavy metals is critical to success of its implementation. However, the majority of studies documenting heavy metal impact on plant functioning have been performed in laboratory or greenhouse settings. We tested the hypothesis that increasing loads of heavy metals in soil reduce photosynthesis and biomass production in trees growing along a soil metal contamination gradient in a naturally re-vegetated urban brownfield. Gas exchange and leaf composition were recorded and compared for Populus deltoides and Populus tremuloides growing in low and high soil metal load areas, while biomass was recorded and compared for both species in low, medium and high soil metal load areas. Heavy metals were found to have minimal impact on photosynthesis of either species. In terms of biomass, only total branch weight (TBW) and leaf area (LA) differed significantly between metal loads, though the difference was largely attributable to variation in diameter at breast height (DBH). Furthermore, TBW and LA values for P. deltoides did not decrease with increasing metal load. Metal load had minimal effect on the relationship between tree age and DBH, and no effect on relationships of tree age and height, LA, or total tree mass, respectively. Significant differences between metal loads were found for δ15N (isotopic nitrogen ratio). However, δ15N and leaf nitrogen content (% N) also differed significantly between species, despite no differences in total leaf nitrogen between species or metal loads indicating that both species were able to obtain similar amounts of N, regardless of metal load, which may be related to mycorrhizae. While short-term water use efficiency (WUE) and nitrogen use efficiency were unaffected by metal load, long-term WUE was, though P. tremuloides enhanced and P. deltoides reduced long-term WUE in high metal load. While these findings do not indicate that heavy metals play no significant role for plants living in metal-contaminated environments, heavy metal impacts on plants are likely altered in the field due to site- and species-specific factors such as nutrient availability and mycorrhizae.